Abnormal voltage indicating device



y 14, 1953 w. H. BIXBY 2,645,765

ABNORMAL VOLTAGE INDICATING DEVICE Filed April 25', 1950 2 Sheets-Sheet1 FIG.

menu/amp 19 I INVENTOR w H B/XBY ATTORNEY y 1953 w. H. BIXBY 2,645,765

ABNORMAL VOLTAGE INDICATING DEVICE I Filed April 25, 1950 2 Sheets-Sheet2 FIG. 2

lNl/ENTOR n. H B/XBY ZJ W ALZ'O RNEY Patented July 14, 1953 2,645,765ABNORMAL VOLTAGE INDICATING DEVICE William H. Bixby, Detroit, Mich,assignor to Donald R. Middleton and Stanley M. Hanley, doing business asPower Equipment Company, Detroit, Mich., a copartnership ApplicationApril 25, 1950, Serial No. 158,042

16 Claims. (Cl. 10- 248) Thi invention relates to relay circuits andmore particularly to circuits for controlling the operation of a relayin response to a predetermined change of an alternating supply voltage.The invention may be used, for example, to control the energization ofan electromagnetic relay for openin or closing an alarm circuit forindicating a change of voltage of a current supply source with respectto a predetermined normal voltage. Instead of controlling an alarmcircuit, the electromagnetic relay may also be employed for protectingapparatusto which current is supplied directly or indirectly from thesupply source to prevent damaging the apparatus due to an abnormallyhigh or low voltage of the supply source.

An object of the invention is to provide an improved circuit forchanging in a predetermined sense the current in a current path inresponse to an increase of voltage of a current supply source and alsoin response to a decrease of voltage of the supply source.

Another object of the invention is to provide a circuit arrangement forchanging the current in one current path in a predetermined sense inresponse to a decrease of voltage of a current supply source below aminimum voltage of a desired voltage range and for changing the currentin another current path in said predetermined sense in response to anincrease of voltage of said current supply source above a maximumvoltage of said voltage range.

In an embodiment of th invention herein shown and described for thepurpose of illustration, there are provided a circuitcomprising athermistor or other resistance device the resistance of which changes ina consistent, non-linear manner with change of current through thede- Ivoltage. Such an arrangement is disclosed in my United States Patent No.2,486,250 granted October 25, 1949, Means are provided for adjusting theamplitudes of the pulsating voltages with respect to the amplitude ofthe supply voltage. The two pulsating voltages are combined with analternating voltage derived from the source voltage so that the voltagepulses are opposed to successive half cycles, respectively, of thealternating voltage. The amplitudes of the pulsating voltages and thederived alternating voltage are such as to give a resultant voltagewhich is substantially zero amplitude when the voltage of the source hasa predetermined amplitude and which increases in amplitude in responseto an increase of the source voltage and also in response to a decreaseof the source voltage. The reultant voltage has one polarity when thesourc voltage rises above the predetermined value and the oppositepolarity when the'source voltage falls below the predetermined value.This rsultant voltage is rectified and the rectified pulsating voltageis combined with an alternating voltage in the gridcathode circuit ofeach of a second pair of space current devices so that the pulses of therectified pulsating voltage are opposed to the half cycles of thealternating voltage in the control gridcathode circuit of each spacecurrent device when the anode of the device is positive with respect toits cathode, the anode cathode voltag of each space current tube alsobeing supplied from the alternating-moment source. The energization ofan electromagnetic relay connected in the space current circuits of thesecond pair of space current devices will thus decrease in response toan increase and also in response to a decrease of the voltage of thealternating-current source to cause the armatureof the relay to bereleased. The release of the relay armature may cause the completion ofan energizing circuit for an indicating lamp or othr alarm device, forexample.

In a modified embodiment of the invention, two electromagnetic relaysare provided, one for changing the 'energization of an indicating orprotective device in" response to an increase of the supply sourcevoltage above a maximum voltage ofra selected normal voltage range andthe other for changing the energization of an indi eating or protectivedevice in response to a decrease of the supplysource voltage below aminimum value of the normal voltage range. Pulsating voltages areproduced as described in the preceding paragraph and the pulsatingvoltages are combined with an unsymmetrical alternating voltage derivedfrom the source and in "opposed phase with respecttl'iereto in thecontrol electrode-cathode circuit of each of four space current devices.The relationship of the unsymmetrical alternating voltage and thepulsating voltag s in the grid-cathode circuits of one pair ofthesespace current devices is such that the space currents of the devicesdecreases in responce to a decreae of voltage of the source to cause therelease of the electromagnetic relay which is energized by said spacecurrents. The relationship of the unsymmetrical alternating voltage andthe pulsating voltages in the gridcathode circuits of the remaining pairof space current devices is such that the space currents of the devicesdecrease in response to an increase of voltage of the source to causethe release of the remaining electromagnetic relay. Preferably each ofthe unsymmetrical alternating voltages is formed by adding to halfcycles of one polarity of a first symmetrical alternating voltage of acertain amplitude, half cycles of a second symmetrical alternatingvoltage of a smaller amplitude to thereby increase the amplitude ofalternate half cycles of the unsymmetrical voltage and by subtractingfrom half cycles of opposite polarity of the first symmetricalalternating voltage half cycles of the second symmetrical voltage tothereby reduce the amplitude of the remaining half cycles of theunsymmetrical voltage. The amplitude of the smaller amplitudealternating voltage may be varied to control the voltage range of thealternating-current source for which both electromagnetic relays areactuated so that one relay releases its armature to produce anindication when the source voltage rises above the maximum value of saidrange and so that the other relay releases its armature to produce anindication when the source voltage decreases below the minimum value ofsaid range.

Fig. 1 of the accompanying drawing is a schematic view of an alarmcircuit embodying the invention; and

Fig. 2 is a schematic view of a modification of the alarm circuit ofFig. 1.

Referring to Fig. 1 of the drawing, there is provided a transformerhaving a primary winding It! connected to an alternating-current supplysource II and a plurality of secondary windings i2, i3, 54, I5, I3 andI1. Across transformer winding I2 are connected in series a resistor I3and a thermistor I9 having the operating characteristic that isresistance decreases in response to an increase of alternating currentflowing therethrough at such a rate that the voltage across thethermistor decreases. Thermistors are described, for example, in BellLaboratories A Record, December 1940, page 106 et seq. potentiometer 20is connected across a portion of transformer winding I3, the variabletap of the potentiometer being connected to the common terminal ofresistor I8 and thermistor I9.

There is provided a twin-triode space current tube ZI comprising spacecurrent triodes 22 and 23 each having an anode, a. cathode and a controlelectrode. The control electrodes of triodes 22 and 23 are respectivelyconnected through resistors 24 and 25 to terminals 43 and 44 oftransformer winding I3. Space current is supplied to triode 22 fromtransformer winding I4 through a circuit comprising a resistor 26 andspace current is supplied to triode 23 from transformer winding Ithrough a circuit comprising a resistor 21. A common terminal ofresistors 26 and 27 and the cathodes of triodes 22 and 23 isconductively connected to a common terminal of thermistor I3 andtransformer winding I2 to complete the control grid-cathode circuits oftriodes 22 and 23. The transformer taps 43 and 44 are chosen to providethe proper operating biases for triodes 22 and 23 when the anodes of therespective triodes are positive with respect to the cathodes. Thevoltage measured from the tap of potentiometer 20 to the point a whichis electrically mid-way between the terminal 43 and 44 is substantiallyequal to the voltage across thermistor I9 when the voltage of source IIis at its normal value so that the voltage measured from the tap ofpotentiometer 23 to terminal 44 is less than the voltage acrossthermistor I9 and the voltage measured from the tap of potentiometer 20to terminal 43 is greater than the voltage across thermistor I9. Thegrid of each triode will thus be negative with respect to its cathodewhen its anode is positive with respect to the cathode.

There is provided a bridge-type full wave rectifier 30 having a resistor3I connected across its output terminals. The input circuit of rectifier30 comprises in series resistors 26 and 2'! and a portion of secondarytransformer winding I5. A twin-triode space current tube 32 comprisingtriodes 33 and 34 is connected as a full wave rectifier for rectifyingcurrent supplied from transformer winding l. and for supplying therectified current to the winding of an electromagnetic relay 35 havingan armature 35, the end terminals of winding I! being connected to theanodes of triodes 33 and 34, respectively, and a mid-tap of winding llbeing connected through relay 35 to the cathode of triodes 33 and 34. Acircuit completed in response to th release of the armature 36 of relay35 comprises an indicating device such as lamp 3? and a source ofenergizing current for the lamp such as battery 38.

A potentiometer 49 is connected across secondary transformer winding l8.Resistors M and 42 in series are provided in a current path connectingthe variable tap of potentiometer 4!! and a common terminal of windingI6 and potentiometer 46. The control electrode-cathode circuit of triode33 comprises resistors 45, M and 3I in series and the controlelectrode-cathode circuit of triode 34 comprises resistors 45, 42 and 3!in series. Where it is desired to delay the response of relay 35 tosudden fluctuations in voltage, a capacitor 47 may be comiected in apath across the relay winding. To avoid high frequency oscillations inthe circuit, a capacitor 48 of very small capacitance is provided in apath connecting the cathode of triode 34 and the common terminal ofresistors 42 and 46.

An increase of the voltage of source II results in a decrease of voltageacross thermistor l!) in addition to a voltage increase across theportion of the transformer winding I3 which is in the controlelectrode-cathode circuits of triodes 22 and 23. Therefore, duringhalf-cycl periods of the alternating-current source II when triode 22 isconducting space current, an increase of the voltage of source II, forexample, results in the control grid of triode 22 becoming relativelymore negative with respect to its cathode to cause the current flowingthrough resistor 26 to decrease. During half cycles of oppositepolarity, an increas of voltage of source l I results in the controlelectrode of triode 23 becoming relatively more positive with respect toits cathode to cause the space current flowing through resistor 27 toincrease.

The pulsating voltages across resistors 26 and 2! are opposed in phasewith respect to and have predetermined amplitudes with respect to thealternating voltage from winding I5 in the input circuit of rectifier30. The opposed pulsating and alternating voltages may havesubstantially equal amplitudes when the voltage of source II has acertain normal value so that the output voltage of rectifier 30 is equalto zero. Then, if it is desired to bring the output voltage of rectifier30 to this same value, zero, for a higher voltage of source it is merelyrequired to adjust potentiometer to increase the voltage between itsvariable tap and point a. of winding 13. The voltage impressed acrossthe input terminals of rectifier 3|] and the voltage across resistor 3|connected to the rectifier output terminals are then each substantiallyzero. The voltages across resistors 4| and 42 thus make the controlgrids of triodes 33 and 34 positive with respect to the cathodes tocause suificient current flow through relay winding 35 to cause therelay to open the energizing circuit for lamp 31.

When the voltage of source rises above the predetermined amplitude, thepulsating voltage across resistor 26 decreases to a value less than theamplitude of the concurrent half-cycle pulses across the portion ofwinding l5 which is in the input circuit of rectifier 30 and thepulsating voltage across resistor?! increases to a value greater thanthe amplitude of the concurrent half-cycle pulses across the portion ofwinding l5. A pulsating voltage is thus impressed upon the input circuitof rectifier 30. When the voltage of source decreases, the pulsatingvoltage across resistor 26 increases to an amplitude greater than thevoltage across the portion of winding l5 and the pulsating voltageacross resistor 2'! decreases to an amplitude less than the voltageacross the portion of winding I5; -A pulsating voltage of oppositepolarity with respect to the pulsating voltage produced when the sourcevoltage rises is thus impressed upon the input or rectifier 30. Therectified'output voltage across resistor 3| has a polarity such as tomake the control electrodes of triodes 33 and 34 relatively morenegative with respect to the cathodes to cause the current in relay 35to decrease. The increase or decrease of the voltage of source H fromthe predetermined normal value which is required to cause the armatureof relay 3B to'release may be varied by adjusting the potentiometer 40to change the voltages across resistors 4| and 42. An increase of thevoltage acros'sfresistors 4| and 42, for example,'will effect a changein operation of the circuit such that a larger increase or decrease ofthe voltage of source H will be required to effect the release of thearma-j ture of relay 36 to thereby cause the energization of the lamp31. The armature 36 of relay 35 thus releases to cause the energizationof lamp 3? when the line voltage increases above the maximum voltage ofa certain desired voltage range and also when the line voltage decreasesbelow the minimum voltage of the voltage range.

The portions of the circuit shown in Fig. 2 which are similar tocorresponding portions of Fig. 1 are identified by the samedesignations. There is provided a twin-triode space current tube 52having triodes 53 and 54 the anodes of which are connected to the endterminals, respectively, of a secondary transformer winding 50. Themid-tap of transformer winding 'is connected through the Winding of anelectromagnetic relay 55 to the cathodes of triodes 53 p and 54, acondenser '51 being connected in a shunt path across the relay Winding.The release of the armature 56 of relay 55 completes an energizingcircuit from battery 58 to an indicator lamp 59. There is provided atwin-triode tube 62 having triodes 63 and 64 the'anodes of which aresimilarly connected to the end terminals of a secondary transformerwinding 5|. The mid-tap of transformer winding 5| is connected throughthe winding of an electromagnetic relay 65 to the cathodes of triodes 63and 64, a condenser 61 being connected across relay winding. The releaseof the armature 66 of relay 65 completes an energizing circuit frombattery 68 to an indicating lamp 69.

A potentiometer H1 is connected across a portion e--c of transformerwinding |5. Similar re- .sistors H and T2 are connected in series acrossa variable portion of potentiometer 10 between the variable tap of thepotentiometer and the terminal connected to terminal 0 of thetransformer Winding. The common terminal of resistors H and 12 isconnected to the cathodes of triodes E3 and 64. The remaining terminalof resistor H is connected through a resistor 84 to the controlelectrode of triode 53 and the remaining terminal of resistor 12 isconnected through a resistor 35 to the control electrode of triode 54. Acondenser 86 is provided in a path connecting the cathode of triode 54and a common terminal of resistor 72 and 85.

A potentiometer 3|), similar-to potentiometer 10, is connected across aportion fd of transformer winding [4. Similar resistors 8| and 82 inseries are connected across a variable portion or potentiometer 30between the variable tap of the potentiometer and the terminal connectedto terminal d of transformer winding M. The variable taps ofpotentiometers l0 and are mechanically connected so that, preferably,the voltage across resistors 7| and 72 is at all times equal to thevoltage across resistors BI and 82. The common terminal of resistors BIand 82 is connected to the cathode of triodes 53 and 54. The otherterminal of resistor 8| is connected through a resistor 81. to thecontrol grid of triode 53 and the other terminal of resistor 82 isconnected through a resistor 88 to the control grid of triode 64. Acondenser 89 is provided in a path connecting the cathode of triode 64and a common terminal of resistors 82 and 88.

For the purpose of explaining the operation of the circuit, let it beassumed that potentiometers 10 and are set so that the variable taps areat the potentials of points 0 and d, respectively. There will then bezero voltage across resistors H and E2 and across resistors 8! and 32.Let it further be assumed that the setting of potentiometer 29 and thevoltage of source aresuch that the voltage between the movable tap ofthe potentiometer 29 and point a of transformer vinding I3 is equal tothe voltage across thermisto'r l9; Under these conditions, during halfcycle periods when the anode of triode 53 is positive with respect toits cathode, there will be impressed upon the grid-cathode circuit oftriode 53 half cycles of the voltage across the portion ec oftransformer winding i5 and, in opposition thereto, the voltage pulses ofequal amplitude across resistor 28, the voltage across resistor 2'!being zero during these half-cycle periods. Similarly, during half-cycleperiods when the anode of triode 54 is positive with respect to itscathode, there will be impressed upon the gridcathode circuit of triode54 half cycles of the voltage e-c and, in opposition thereto; thevoltage pulses of equal amplitude across resistor 21. The control gridsof triodes 53 and 54 will then be at the same potential as the cathodesand suihcient space current will flow through the winding of relay 55 tomaintain the relay in the operated condition. A slight increase ofvoltage of the source i! above the assumed normal value will cause thevoltage pulses across resistor 23 to decrease in amplitude and thevoltage pulses across resistor 21 to increase in amplitude, therebmaking the control grids of triodes 53 and 54 sufficiently negative withrespect to the cathodes to cause the current in the winding of relay 55to be reduced and to cause the relay armature 55 to be released. Theresulting energization of lamp produces an indication of the high linevoltage condition.

For the conditions stated in the preceding parag p11, when the anode oftriode G3 is positive with respect to its cathode, there will beimpressed upon the grid-cathode circuit of triode 5 3 hall cycles of thevoltage e-c and, in opposition thereto, the voltage pulses of equalamplitude across resistor 26. When the anode of triode is positive withrespect to its cathode, there will be impressed upon the grid-cathodecircuit of triode 8 2 half cycles of the voltage e-c and, in opposition'iereto, the voltage pulses of equal an litude across 'esistor 21. Thepolarities of the component voltage in the gridcathode circuits oftriodes E33 and 64, however, are reversed with respect to the polaritiesof the corresponding vol ages in the grid-cathode circuits of triodes 53and 54. A slight decrease of the voltage of the source H below theassumed normal value will cause the voltage pulses across resistor 23 toincrease in amplitude and the voltage pulses across resistor 22' todecrease in am plitude, thereby making the grids of triodes 63 and i lsufficiently negative with respect to the cathodes to cause the armatureof relay 56 to be released. Lamp 69 is thus energized to pro duce anindication of the low voltage condition.

It will be noted that as the taps of potentiometers 88 and are moved byequal amounts toward positions and 6, respectively, for any positions ofthe taps, the voltage between the common terminal of resistors Bi and 82and the common terminal of resistors H and 72 will be equal to thedifference of the voltage e-c and the voltage across resistor 26 duringhalf-cycle periods when the anodes of triodes 22, 53 and 63 positivewith respect to their cathodes and said voltage will be equal to thedifference of the voltage c-c and the voltage across resistor 27 whenthe anodes of triodes 23, 54 and 64 are posiave with respect to theircathodes. The grid-cathode voltages of each of triodes 53, 54 63 and isthe voltage between the common terminal of resistors 8! and and thecommon terminal of resistors H and "i2 plus a bias voltage across oneor" the resistors ll, l2, 8!, 82, the bias voltage having a polaritysuch as to make the grid relatively more positive with respect to thecathode when the anode is positive with respect to the cathode. Thevoltages across resistors ll, l2, :3! and 82 are the added biasingvoltages for triodes 53, 53, 5 2 and 64, respectively, these biasingvoltages being equal and adjustable by moving the taps of potentiometersl0 and 80. An increase of these biasing voltages makes necessary arelatively larger decrease of voltage across resistor 25 and arelatively larger increase of voltage across resistor 21 to effect therelease of relay An increase of these biasing voltages also makesnecessary a relatively larger increase of voltage across resistor 25 anda relatively larger decrease of voltage across resistor 2'! to effectthe release of relay 65. In other words, moving the potentiometer tapsfrom (1 toward 1 and from 0 toward e increases the normal voltage rangefor which relays 55 and 65 remain operated, the relays, respectivelybeing released only when the source voltage goes above and below themaximum and minimum values, respectively, of the normal voltage range.

If for one setting of potentiometers :9, relay 65 should release whenthe voltage of source H is 98 per cent of a certain predeterminedvoltage and the release of relay 55 should occur when the voltage ofsource I! is 102 percent of the predetermined voltage, for example,increasing the bias voltages by readjusting potentiometers I0, 80 couldcause the relay 65 to release at 96 per cent of the predeterminedvoltage and the relay 55 to release at 104 per cent of the predeterminedvoltage. Thus the setting of potentiometers 10, 80 determines the rangebetween the low voltage indication produced by lamp B9 and the highvoltage indication produced by lamp 59 while the setting ofpotentiometer 20 determines the voltage level of the center point ofthis range, the two adjustmerits being almost independent of one anotheras far as their effects are concerned.

What is claimed is: 1 The combination with a source of alternatingvoltage the amplitude of which may change, of means for deriving fromsaid source a symmetrical alternating voltage substantially proportionalto the voltage of said source, means for deriving from said sourceduring periods of one polarity thereof a first pulsating voltage theamplitude of which decreases by a larger amount than the amplitudeincrease of said derived al ternating voltage in response to an increaseof voltage of said source, means for deriving from said source duringperiods of opposite polarity thereof a second pulsating voltage theamplitude of which increases by a lar er amount than the amplitudeincrease of said derived alternating voltage in response to an increaseof voltage of said source, and means for combining said derivedalternating and pulsating voltages with each of said pulsating voltagesin phase opposition to said derived alternating voltage to produce aresultant voltage the amplitude of which changes in a predetermineddirection when the voltage of said source either increases or decreases.

2. In combination, a space current device having an anode, a cathode anda control electrode, a first circuit connecting said anode and saidcathode, means for causing current to flow in said first circuit, analternating-current supply source the voltage of which may vary, asecond 7 circuit connecting the control electrode and cathode of saiddevice, and means for deriving from said supply source and impressingupon said second circuit a voltage for causing the current in said firstcircuit to change in a predetermined sense in response to a voltageincrease of said supply source to a certain relatively high voltage andfor causingthe current in said first circuit to change in saidpredetermined sense in response to a voltage decrease of said supplysource to a certain relatively low voltage.

3.. In combination, a space current device havmg an anode, a cathode anda control electrode, an alternating-current supply source the voltage ofwhich mayvary, a space current circuit for said device comprising afirst source oI alternating voltage derived from said supply source,means for deriving from said source a second voltage the amplitudeofwhich increases in response to an increase of said supply voltage abovea predetermined voltage and the amplitude of which 9 increases inresponse to a decrease of said supply voltage below said predeterminedvoltage and means for impressing said second derived voltage upon acircuit connecting-said control electrode and said cathode forcontrolling. the amplitude of said space current.

4. In combination, a space current device having an anode, a cathode anda control electrode, an alternating-current supply source the voltage ofwhich may vary, means for supplying current from said source to a spacecurrent circuit connecting said anode and said cathode, means forderiving from said source a voltage the amplitude of which increases inresponse to an increase of said supply voltage above a predeterminedvoltage and the amplitude of which increases in response to a decreaseof said supply voltage-below said predetermined voltage, means forselecting a desired predetermined voltage above and below which saidderived voltage increases, and means for impressing said derived voltageupon a circuit connecting said control electrode' and said cathode forcontrolling the amplitude of said space current.

5. In combination, a space current device having an anode, a cathode anda control electrode, I

means for supplying current from an alternating-current supply source toa space currentcircuit connecting said anode and said cathode, means forderiving from said supply source avoltage the amplitude ofWhich'increases in response to an increase of said supply voltage from afirst voltage to a second voltage and the amplitude of which increasesin response to a decrease of said supply voltage from said first voltageto a third voltage, means for adjusting said second and third voltagesrelative to said first voltage to determine the voltage range ofsaidsupply source above and below which said derived voltage increases,and means for impressing said derived voltage upon a circuit connectingsaid control electrode and said cathode for controlling the amplitude ofsaid space current. I

6. A combination in accordance. with claim 5 v in which 'is providedmeans for adjusting said a first voltage to a second voltage and theamplitude of'which increases inthe opposite sense in response to adecrease of said supply voltage from said first voltage to a thirdvoltage, means to impress said derived voltage upon a circuit connectingthe control electrode and cathode of said first device with a polarityto cause. the space current of said first device to decrease when saidsupply voltage increases from said first voltage to said second voltage,and means to impress said derived voltage upon a circuit connecting thecontrol electrode and cathode of said second device with an oppositepolarity to cause the space current of said second device to decreasewhen said supply voltage decreases from said first voltage to said thirdvoltage.

8. A combination in accordance with claim 7 in which there are provideda first means connected in the space current path of said first devicefor producing an indication when said suptrode, means for impressingupon the control electrode and cathode of said first device a voltagederived from said source for causing the current supplied to said firstcurrent responsive means to be reducedto a predetermined value inresponse to an increase of said supply voltage to a voltage above acertain normal range, and means for impressing upon the controlelectrode and cathode of said second device a voltage derived from saidsource for causing the current supplied to said second currentresponsive means to be reduced to a predetermined value in response to adecrease of said supply voltage to a voltage below said normal range.

10. The combination with an alternating-current supply source-thevoltage of which may change, of means for deriving from said supplysource during periods of one polarity thereof afirst pulsating voltagethe amplitude of which decreases in response to a voltage increase ofsaid source but at a higher rate, and vice versa, means for derivingfrom said supply source during periods of opposite polarity thereof asecond pulsating voltage the amplitude of which increases in response toa voltage increase of said source but at a higher-rate, and vice versa,a first full wave rectifier, means for combining said pulsating voltageswith an alternating voltage derived from said source in the inputcircuit of said full wave rectifier, said pulsating voltages being inopposition to half cycles of said derived alternating voltage,resistance means having two end terminals and a mid-terminal, means forimpressing across said resistance means an alternating voltage ofvariable amplitude and fixed phase derived from said source, a secondfull wave rectifier comprising two space current devices each having ananode, a cathode and a control electrode for rectifying current fromsaid alternating-currentsource, means for connecting the mid-terminal ofsaid resistors to the negative output terminal of said first full waverectifier, means for connecting the cathodes of said space currentdevices to the positive output terminal of said first full waverectifier, and means for connecting the end terminals of said resistancemeans to the control electrodes of said space current devices,respectively, thereby controlling the output current of said second fullwave rectifier.

11. A combination in accordance with claim 10 in which there areprovided an indicating device for producing an indication in response toabnormally high and abnormally low voltages of said supply source and anelectromagnetic relay energized by the rectified output current of saidsecond full Wave rectifier for controlling the energization of saidindicating device.

12. The combination with an alternating-current supply source, of atransformer having a primary winding connected to said source and aplurality of secondary windings, a full wave rectifier comprising afirst and a second space current device for rectifying current from saidsource supplied through a first of said secondary windings, each of saidspace current devices having an anode, a cathode and a controlelectrode, a first resistor having a terminal connected to a terminal ofa second secondary Winding, a first potentiometer connected across saidsecond secondary winding and having a variable tap, means for connectingsaid variable tap to the control electrode of said first device, meansfor connecting a terminal of said second secondary winding to thecontrol electrode of said second device, a second resistor having aterminal connected to a second terminal of said first resistor, a thirdsecondary winding having a first terminal connected to a second terminalof said second resistor, a second potentiometer connected across saidthird secondary winding and having a variable tap, means formechanically connecting the variable taps of said potentiometers,resistance means connecting the second terminal of said third secondarywinding and the variable tap of said second potentiometer, saidresistance means having a mid-tap, means for connecting said midtap tothe cathodes of said devices, means for supplying current from saidsupply source to said first resistor to set up across said resistorduring half-cycle periods of one polarity of said source a pulsatingvoltage the amplitude of which decreases in response to a voltageincrease of said source and vice versa, and means for supplying currentfrom said supply source to said second resistor during half-cycleperiods of opposite polarity of said source a pulsating voltage theamplitude of which increases in response to a voltage increase of saidsource and vice versa, each of said pulsating voltages being inopposition to the voltage supplied by said second and third secondarywindings in the control electrode-cathode circuits of said space currentdevices.

13. In combination, a transformer having a primary winding connected toan alternating current supply source and a plurality of secondarywindings, a thermistor and a first resistor connected in series to afirst of said secondary windings, a first potentiometer connected acrossa portion of a second of said secondary windings, means for connectingthe variabletap of said potentiometer toa common terminalof saidthermistor and said first resistor, a first and a second space currentdevice each, having. an anode, a

cathode and a control electrode, a second and a third resistor, meansfor connecting a terminal of each of said second and third resistors tosaid cathodes and to a common terminal of said thermistor and said firstsecondary winding, means for connecting said control electrodes to saidsecond secondary winding, a space current circuit for said first spacecurrent device, comprising a third of said secondary windingsv and saidsecond resistor, a space current circuit for said second space currentdevice comprising a fourth of said secondary windings andsaid thirdresistor, a full wave rectifier, having input and output terminals,means for connecting one of said input terminals to a common terminal ofsaid second resistor and. said third. secondary winding, means forconnecting the other of said input terminals to said fourth secondarywinding, a fourth resistor connected to the output terminals of saidrectifier, a third anda fourth space current device each having ananode, a.

cathode and a control electrode, a second potentiometer connected acrossa fifth of said sec- 1.2 ondary windings, a fifth and a sixth resistorhaving a common terminal connected to a first terminal of said fourthresistor, means for connect,- ing the other terminal of said fifthresistor to the variable tap of said second potentiometer,

means for connecting the other terminal of said sixth resistor to acommon terminal of said second potentiometer and said fifth secondarywinding, means for connecting the terminals of said fifth and sixthresistors other than said common terminal to the control electrodes ofsaid third and fourth space current devices, respectively, means forconnecting the cathodes of said third and fourth space current devicesto the second terminal of said fourth resistor, means for connecting theanodes of said third and fourth devices to the end terminals,respectively, of a sixth of said secondary windings, current responsivemeans, and means for connecting said current responsive means in a pathconnecting the oathodes of saidvthird andfourth devices and amidterminal of said sixth winding.

14. In combination, a transformer having a primary winding connected toan alternatingcurrent supply source and a plurality of secondarywindings, a thermistor and a. first resistor connected in series to afirst of said secondary windings, a first potentiometer connected acrossa portion of a second of said secondary windings, means for connectingthe variable tap of, said potentiometer to the common terminal of saidthermistor and said first resistor, six space current devices eachhaving an anode, a cathode and a control electrode, a second and athirdresistor having a common terminal connected to the oathodes ofafirst and a second of saidspace current devices andto a common terminalof. thermistor and said first secondary winding, means for connectingthe control electrodes of said first and second devices to said secondsecondary winding, a space current circuit for said, first devicecomprising a third of said secondary windings and said second resistor,a space current circuit for said second device comprising a fourth ofsaid secondary windings and'said third resistor, a second' potentiometerconnected to a common terminal of said third secondary winding and saidsecond resistor and to another terminal of said third secondary winding,a third potentiometer connected to a'common terminal of said fourthsecondary winding and said third resistor and to another terminal ofsaid fourth secondary winding, means for mechanically connecting thevariable taps of said second and third potentiometers, a fourth and afifth resistor having a common terminal connected to the cathodes of athird and a fourth of said space current devices, means for connectingthe other terminal of said fourth resistor to the variable tap of saidsecond potentiometer, means for connecting the other terminal of saidfifth resistor to the common terminal of said third secondary'windingand said second resistor, a sixth and a seventh resistor having a commonterminal connected to the oathodes of a fifth and a sixth of said space.currentv devices, means for connecting the other terminal. of said sixthresistor to the: variable tap of said third potentiometer, means forconnecting the other terminal of said seventh resistor to saidv otherterminaliof said fourth secondary winding, means for connecting theterminalsof said fourth and fifth resistors other than their. commonterminal to the control electrodes of said fifth and sixth space currentdevices, respectively, means for connectingtheiterminals of said sixthand seventh resistors other than their common terminal to the controlelectrodes of said third and fourth space current devices, respectively,a first electromagnetic relay having a winding in a current pathconnecting the cathodes of said third and fourth space current devicesand a mid-terminal of a fifth of said secondary windings, means forconnecting the end terminals of said fifth winding to the anodes,respectively, of said third and fourth devices, means for connecting theend terminals of a sixth of said transformer windings to the anodes,respectively, of said fifth and sixth space current devices, and asecond electromagnetic relay in a current path connecting the cathodesof said fifth and sixth devices and a mid-terminal of said sixthsecondary winding.

15. In combination, a current responsive means, means for supplyingcurrent from an alternatingcurrent supply source to said currentresponsive means, and means for decreasing by a predetermined amount thecurrent supplied to said current responsive means in response to apredetermined voltage increase of said supply source above a certainnormal voltage and also in response to a predetermined voltage decreaseof said supply source below said normal voltage.

16. A combination in accordance with claim 15 in which means areprovided for changing said predetermined voltage increase and saidpredeterined voltage decrease required for decreasing the currentsupplied to said current responsive means by said predetermined amount.

WILLIAM H. BIXBY.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,642,710 Affel Sept. 20, 1927 2,150,265 Conover Mar. 14, 19392,197,868 Knowlton Apr. 23, 1940 2,367,509 Knowlton Jan. 16, 19452,369,678 McWhirter Feb. 20, 1945 2,377,506 McWhirter, et al. June 5,1945 2,391,532 Wilmotte Dec. 25, 1945 2,435,572 Bixby I Feb. 10, 19482,441,359 Jones May 11, 1948 2,442,786 Somers June 8, 1948 2,470,067Callender et al. May 10, 1949 2,472,042 Davies May 31, 1949 2,475,356Meschter July 5, 1949 2,466,250 Bixby II Oct. 25, 1949

